ADVICE needed: Rear brakes locking up
 

Now Ive done some tests and came to the conclusion that my driver side rear brake is sticking. It isnt the e-brake, we checked that. It seems to be something with the caliper or brake lines. I tried lubing the caliper bolts and putting them back in, but that didnt work too well, the brake still stuck., we tried bleeding the brake, that also, did not work. Any ideas are welcome

rebuild the piston

thanks :) but im trying not to rebuild them for now...;p